1. Field of the Invention
The present invention relates to an electromagnetic fuel injection valve utilized mainly in the fuel supply system of an internal combustion engine.
2. Description of the Related Art
In recent years, while restrictions on exhaust gas from a vehicle and the like have been tightened, there has been required improvement in atomization of a fuel injected through a fuel injection valve, and hence various kinds of studies about atomization have been made. In the prior arts disclosed in Japanese Patent Application Laid-Open No. 2003-336562 and Japanese Patent Application Laid-Open No. 2003-336563, a fuel injection valve is configured in such a way that respective guide paths are provided for the injection holes, and a fuel rectified and accelerated by means of the guide path flows into a swirl chamber. The fuel forms a swirling flow in the swirl chamber and swirls within the injection hole; then, a fuel spray injected through the outlet of an injection hole plate becomes hollow and cylindrical fuel spray, so that atomization is allegedly facilitated.
Additionally, in prior arts disclosed in Japanese Patent Application Laid-Open No. 2006-2620, Japanese Patent Application Laid-Open No. 2006-336577, and Japanese Patent Application Laid-Open No. 2007-182767, the fuel flow is controlled based on the relationship between the shape of the fuel chamber and the position of the injection hole and a swirling flow is induced at the injection hole inlet, so that atomization is allegedly facilitated.
Meanwhile, in the prior arts disclosed in Japanese Patent Application Laid-Open No. 2003-336562 and Japanese Patent Application Laid-Open No. 2003-336563, a fuel injection valve is configured in such a way that respective guide paths are provided for the injection holes, and a fuel rectified and accelerated by means of the guide path flows into a swirl chamber; therefore, there have been such problems as described below.
[Effect on Flow Rate Characteristics]
In the foregoing prior arts, because the fluid resistance is large at the downstream side of a valve seat, the pressure reducing speed is low at the downstream side of the valve seat during the valve body closing process; therefore, because the valve closing delay time in which a valve closing signal is input and then the valve body is completely closed is long, the flow rate dynamic range is deteriorated.
[Effect on Fuel Spray Characteristics]
Because the fluid resistance is large at the downstream side of the valve seat, the fuel spray injected through the injection hole is liable to adhere; therefore, there may be caused a splashing phenomenon in which the fuel that has not been able to separate from the injection hole and has adhered to the endface, of the injection hole plate, in the vicinity of the injection hole outlet is splashed when the next injection is performed, whereby inferior fuel spray is injected outside the target injection zone; as a result, fuel adhesion to various parts of the engine increases, whereby exhaust gas and the controllability in the engine output may be deteriorated.
[Effect of Atmospheric Change]
Under a high-temperature and negative-pressure condition, due to vaporization of part of fuel in a so-called dead volume, a gas-liquid two-layer flow is caused, and the pressure loss is large when the gas-liquid two-layer flow passes through a narrow flow path; in the example of prior art, because the flow path is configured in such a way that the guide path, i.e., a diaphragm is provide from the downstream side of the valve seat to the injection hole, there has been a problem that, due to change in the temperature or the atmospheric pressure, the flow rate characteristics (static flow rate/dynamic flow rate) and the fuel spray characteristics (fuel spray shape/fuel-spray particle diameter) change considerably.
[Production Cost]
Because the speed of the fuel that flows into each swirl chamber depends on the shape of the guide path, the variation in the shape of the guide path largely affects the deviation of the injection amount of the fuel injected through the injection hole; therefore, a guide path having a high-accuracy shape is required, whereby the production cost is raised. When the deviation of the injection amount is large, the shape of the fuel spray varies, whereby, when the fuel is injected in the engine, the adhesion amount in various part of the engine and the distribution of the fuel-air mixture vary; therefore, the variation in combustion may cause an increase in the amount of exhaust gas or a fluctuation of the engine rotation.
In order to reduce the thickness of fuel liquid film so as to atomize the fuel spray, it is required to exert large swirling force on the fuel in the injection hole. In order to reinforce the swirling force in the swirl chamber, it is required to enlarge the offset between the injection hole inlet and the fuel path; thus, the ratio of depth to width of the fuel path becomes large. Accordingly, the machining of the fuel path becomes difficult, and in the case where the fuel path is formed with a press machine, there has been a problem that the lifetime of the die is shortened and hence the production cost increases.
In the case where a multi-hole injector is adopted for the purpose of further atomizing the fuel spray, the diameter of each injection hole becomes small and hence the fuel path becomes narrow, whereby the machining of the fuel path becomes difficult; therefore, in the case where the fuel path is formed with a press machine, there has been a problem that the lifetime of the die is shortened and hence the production cost increases.
In the prior arts disclosed in Japanese Patent Application Laid-Open No. 2006-2620 and Japanese Patent Application Laid-Open No. 2006-336577, a fuel injection valve is configured in such a way that the fuel flow is controlled based on the relationship between the shape of the fuel chamber and the position of the injection hole and a swirling flow is induced at the injection hole inlet; thus, there have been such problems as described below.
[Effect on Fuel Spray Characteristics]
Because the fuel injection valve according to the foregoing prior arts has no swirl chamber and has a flow opposite to the swirling flow, there has been a problem that the swirling flow does not develop sufficiently and hence the atomization is not facilitated.
In the mechanism in which swirling force is exerted on a fuel so as to atomize the fuel, it is important that the fuel is pressed against the inner wall of the injection hole while swirling within the injection hole so that the fuel is not filled in the injection hole but becomes thin liquid films and is injected in a hollow form through the injection hole outlet, and then the hollow liquid films spread due to centrifugal force, so that the liquid films become thinner, and due to shearing force exerted by air, the liquid films are split. With regard to the shape of a fuel chamber according to the prior arts, at the upstream side of the injection hole, there is provided a shape with which the fuel flow separates from the rest, and the separation of the fuel causes a disturbance in the flow. When the injected hollow liquid films spread due to centrifugal force, there exists a disturbance in the fuel flow in the case of the foregoing prior arts; therefore, the liquid film is split, with the thickness thereof kept thick, in process of spreading. There has been a problem that, because the split liquid thread or liquid drop is not likely to further split, the fuel cannot readily be atomized.
[Effect on Variation in Characteristics]
The flow path is made in such a way that, in the fuel chamber at the upstream side of the injection hole, the fuel flow separates from the rest; therefore, there has been a problem that, due to the disturbance in the separated fuel, the flow rate characteristics and the fuel spray characteristics are likely to vary.
[Effect of Atmospheric Change]
Under a high-temperature and negative-pressure condition, the fuel separation makes the fuel tend to boil under reduced pressure; therefore, there has been a problem that, due to atmospheric change, the flow rate characteristics (static flow rate/dynamic flow rate) and the fuel spray characteristics (fuel spray shape/fuel-spray particle diameter) change considerably.
Also in the prior art disclosed in Japanese Patent Application Laid-Open No. 2007-182767, the fuel flow is controlled based on the relationship between the shape of the fuel chamber and the position of the injection hole and a swirling flow is induced at the injection hole inlet; thus, there has been such a problem described below.
[Effect on Fuel Spray Characteristics]
Because the fuel injection valve according to the foregoing prior art has no swirl chamber and has a flow opposite to the swirling flow, there has been a problem that the swirling flow does not develop sufficiently and hence the atomization is not facilitated.